1. Field of the Invention
The present invention relates to a fiber interface shelf. More particularly, it relates to a fiber interface shelf that interfaces between subscriber lines and asynchronous transfer mode type (ATM) switch modules, or interfaces between ATM switch modules and interconnecting transmision paths, that is, various kinds of switches, such as a toll switch or the like, on a broadband-ISDN (B-ISDN) system.
2. Description of the Related Art
Commercial use of broadband-ISDN systems has started, and ATM switches employed for the systems have actively been developed in recent years.
Referring now to FIG. 9, a structural example of a broad-band-ISDN system is shown. Shown are ATM switches 80 to 82 that are connected by transmission highways, for example, optical fiber lines 801 to 803. The ATM switches are also connected via a concentrator 83, or directly connected to subscriber lines 804 to 807.
FIG. 10 is a structural example of the ATM switch. In FIG. 10, an ATM switch module 800 is connected to subscribers or users via fiber interface shelves 90. Further, the ATM switch module 800 is connected to ATM toll switches via the fiber interface shelves 90.
More particularly, the fiber interface shelves 90 are connected via high speed transmission paths, such as 622 Mbps highways (SONET STS-3) or the like, to the ATM switch module 800. Speed of the highway is prescribed in the ITU-T, the Bell Core standard or the like.
Each of the fiber interface shelves 90 generally comprises fiber interface cards and a fiber interface common card. The fiber interface card extracts ATM cells employing 53 bytes on a payload of an ATM signal frame format.
The fiber interface common card has a function for attaching a routing selection signal (TAG) of one bite that is stored in a table, not shown in the diagram, based on a Virtual Path Identifier (VPI) and a Virtual Channel Identifier (VCI) included in the ATM cell, i.e., signals for identifying a vertical channel on a physical line, and sending the ATM cell attached with the routing selection signal to the ATM switch module 800 to control the switching of routing signals in the ATM switch module 800.
Subscribers connected via the fiber interface shelves 90 are connected to subscriber transmission paths having various speed variations, such as 45 Mbps to 622 Mbps or the like. In FIG. 10, details of the fiber interface shelf 90 are not shown in the diagram, and a plurality of low speed subscriber transmission paths are multiplexed by a multiplexer, not shown in the diagram. Accordingly, the subscriber transmission paths are interfaced with the speed of optional fiber lines linked to the ATM switch module 800.
There is a case where a subscriber transmission path has the same speed as that of a transmission path on the ATM switch module 800. In this case, the subscriber transmission path is not multiplexed, but it is interfaced with optical fiber lines on the ATM switch module 800.
Referring now to FIGS. 11A and 11B, explanation diagrams are shown for illustrating the relationship of connection between the ATM switch module 800 in the ATM switch and the fiber interface cards and the fiber interface common card that form a fiber interface shelf, when the subscriber transmission path has the same speed, for example, 622 Mbps, as that of the optical fiber line on the side of the ATM switch module 800.
Shown are the duplexed ATM switch modules (#0, #1) 800, 800'. The duplexed fiber interface common cards 92, 92' are provided on both the subscriber line side (WEST side) and the interconnecting transmission path side (EAST side) corresponding to the duplexed ATM switch modules 800, 800'.
Further, FIG. 11A illustrates a flow from the side of the subscriber line (WEST side) to the interconnecting transmission path side (EAST side) in an upward direction. FIG. 11B further illustrates a flow from the side of the interconnecting transmission path (EAST side) to the side of the subscriber line (WEST side) in a downward direction.
As the subscriber line is simplex in the example of FIGS. 11A and 11B, a fiber interface card 91 of the subscriber line side is switchably connected to the fiber interface common cards 92, 92', which are provided for working and protection, respectively. The duplexed fiber interface common cards 92, 92' are connected to the duplexed fiber interface cards 91, 91' on the inerconnecting transmission path side of the ATM switch modules 800, 800'.
Fiber interface common cards 92, 92' having a duplexed structure and fiber interface cards 91, 91' are crossed over and switched according to an active (ACT) or standby (STB) mode on the interconnecting transmission path side, to which other toll switches are connected, that is, the EAST side of the ATM switch modules 800, 800'.
The above-described structure is provided for a flow from the subscriber side (WEST side) to the interconnecting transmission path side (EAST side) in the upward direction and a flow from the interconnecting transmission path side (EAST side) to the subscriber side (WEST side) in the downward direction.
FIG. 12 illustrates a diagram for explaining the relationship between ATM switch modules 800, 800' and fiber interface cards 91, 91' and fiber interface common cards 92, 92' that form a fiber interface shelf when employing duplexed subscriber transmission paths.
In FIG. 12, only the upward direction from the subscriber side (WEST side) to the interconnecting transmission path side (EAST side) is shown. However, as well as the case shown in FIG. 11, the downward direction from the interconnecting transmission path side (EAST side) to the subscriber side (WEST side) has the same structure as that of the upward direction.
In FIG. 12, a pair of fiber interface cards 91, 91' are also provided corresponding to the duplexed subscriber lines, and the fiber interface cards 91, 91' are switched and connected to the fiber interface common cards 92, 92' according to a an active (ACT) or standby (STB) mode on the side of subscriber lines. Other connecting forms are the same as those shown in FIG. 11A.
FIG. 13 is a block diagram illustrating an example of a fiber interface shelf when the subscriber side corresponding to FIG. 11A employs a simplex two-channel structure. In FIG. 13, two subscriber lines I and II with the speed of 622 Mbps are respectively connected to each of duplexed fiber interface common cards 92, 92' in the fiber interface shelf, which is enclosed with a broken line in the diagram, via the fiber interface cards 910, 911', respectively.
FIG. 14 is a diagram illustrating an example of the fiber interface shelf when the subscriber line side corresponding to FIG. 12 also employs a duplexed 1+1 structure. In FIG. 14, the duplexed subscriber lines I and I' are connected to the corresponding fiber interface cards 91 and 91', respectively.
Further, the fiber interface cards 91, 91' are connected to the duplexed fiber interface common cards 92, 92'. In FIG. 14, each of the fiber interface common cards 92, 92' selects a main signal on a working path of the duplexed subscriber lines I and I' and sends it to the corresponding ATM switch modules 800, 800'.
The above-described fiber interface common cards 92, 92' shown in FIGS. 13 and 14 are formed as shown in FIG. 15. In FIG. 15, only the structure of the interface common card 92 is shown, as the structure of the card 92' is the same as that of the card 92. The fiber interface common card 92 comprises selecting gates 920 and 921, a controller 922, a signal circuit 923, a multiplexer 924, which inserts an internal communication signal sent from the signal circuit 923 into a main signal, a demultiplexer 925, which branches the internal communication signal sent from the ATM switch module 800 and a Virtual Channel Converter (VCC) 926, which inserts a TAG signal that controls the selection of routing path of signals in the ATM switch module 800.
The selecting gate 920 switches and outputs the main signal on active one of a pair of fiber interface cards 91, 91'. The main signal sent from the ATM switch module 800 is commonly outputted to a pair of the fiber interface cards 91, 91', under the control of controller 922.
Further, the selecting gate 921 has a function for looping back signals sent from the ATM switch module 800, under the control of the controller 922 at a loop-back testing.
Each fiber interface common card has the same structure as shown in FIG. 15, in both the simplex two channel structure mode shown in FIG. 13 and the duplexed structure mode formed of one working line and one protecting line (hereinafter, referred as to a 1+1 duplexed structure) shown in FIG. 14. Both the controller 922 and the signal circuit 923 can be used to switch the main signal commonly for the both modes.
Accordingly, it is not always necessary to provide the controller 922 and the signal circuit 923 on each fiber interface common card. If the structure shown in FIG. 15 is employed in the cases shown in FIGS. 13 and 14, circuit structures become redundant and the miniaturization of a device cannot be improved.
When the fiber interface common card having a simplex two-channel structure shown in FIG. 13 is switched to be used as the card having a 1+1 duplexed structure shown in FIG. 14, one set of fiber interface common cards 92, 92' is not used as shown in FIG. 14.
Furthermore, as apparent from FIGS. 11A, 11B and 12, the fiber interface shelf provided on the subscriber line side of the ATM switch modules 800, 800' can have the same structure as that of the fiber interface shelf provided on the interconnecting transmission path side of the ATM switch modules 800, 800'. In general, the subscriber transmission path has a simplex structure, and the interconnecting transmission path has a duplex structure.